The present invention generally relates to M-S (Mid-Side) type sterophonic microphones, and more particularly to an M-S type sterophonic microphone in which a mid microphone unit and a side microphone unit are supported with an effective vibrationproof effect so that unwanted external vibrations are not transmitted to the mid and side microphone units.
Generally, stereophonic microphones may be divided roughly into X-Y type stereophonic microphones and M-S type stereophonic microphones. Both types of stereophonic microphones are reduced to practice, but the M-S type stereophonic microphones are more popularly used. In an M-S type stereophonic microphone, a uni-directional mid microphone unit and a bi-directional side microphone unit are arranged so that main axes of directivities thereof are perpendicular to each other, which main axes are perpendicular to respective diaphragms and pass the center of the respective diaphragms. By obtaining signals corresponding to the sum and the difference of outputs of the two microphone units, it is possible to compose the directivities of the two microphone units and obtain signals of two channels having two new directivities.
The advantage of the M-S type stereophonic microphone is that the localization and width of sound image can be controlled electrically, because the directivity and direction of the main axis thereof can be changed by changing the proportion of the sum and the difference of the outputs of the two microphone units.
Normally, an M-S type stereophonic microphone used in broadcasting station or the like has the following construction. That is, the M-S type stereophonic microphone comprises a stick-shaped casing comprising a mid microphone unit and a side microphone unit. The two microphone units are arranged so that a main axis of the mid microphone unit is perpendicular to the longitudinal axis of the casing and a main axis of the side microphone unit is perpendicular to both the longitudinal axis of the casing and to the main axis of the mid microphone unit. The M-S type stereophonic microphone is used in such a manner that the main axis of the mid microphone unit is directed toward the front. However, a microphone which is mounted and used in a video camera, 8-mm movie camera and the like, must take into account the fact that a sound source which is to be picked up is located in a direction in which a lens of the camera points. But, the microphone which is mounted on the camera generally has a stick shape extending parallel to the optical axis of the lens, so that the microphone is easily accessible in the state where the microphone is mounted on the camera. In this case, the sound source is located in the longitudinal direction of the stick-shaped microphone. Accordingly, in a case where the M-S type stereophonic microphone is to be used as the stick-shaped microhone for use on the camera, the M-S type stereophonic microphone must be mounted on the camera in such a manner that the main axis of the mid microphone coincides with the longitudinal axis of the M-S type steroephonic microphone and the main axis of the side microphone unit extends in a direction perpendicular to the longitudinal axis of the M-S type stereophonic microphone.
On the other hand, vibrations introduced due to causes such as the fact that the camera is operated in a state where an operator grips the camera with his hands, the rotation of a motor and the manipulation of switches, are transmitted to the microphone through a mounting part (microphone mounting shoe) which mounts the microphone on a main camera body of the camera. When such external vibrations are transmitted to the microphone, unwanted noise are mixed into the output of the microphone. Thus, a vibrationproofing member is provided on a part of a microphone body where a microphone unit is supported, in order to obtain a vibrationproof effect.
As a type of a vibrationproof structure, there is a conventional structure in which the uni-directional microphone unit is mounted on a frame by way of a cushion member made from rubber, urethane resin or other sponge material. However, this conventional vibrationproof structure is disadvantageous in that a sufficient vibrationproof effect cannot be obtained. Hence, there is another conventional vibrationproof structure which will be described later on in the specification by referring to drawings. According to this other conventional vibrationproof structure, rubber support rings are used. The support ring integrally comprises three or four arms extending toward the center of the ring from an outer rim thereof, and a support part is integrally provided at an intersection of the arms. Central parts of the front and rear ends of the uni-directional microphone unit are supported by the central support parts of the pair of support rings. The outer rim of the respective support rings are mounted on the frame, and the uni-directional microphone unit is supported within the frame by the pair of support rings in a suspended state. As a result, the uni-directional microphone unit is supported so that the uni-directional microphone unit is movable in the longitudinal direction of the microphone.
According to this other conventional vibrationproof structure which uses the support rings, the external vibrations which are transmitted from the camera or the like are absorbed to a certain extent by the support rings. Hence, the vibrationproof effect can be obtained to a certain extent. However, due to the provision of the arms, the central support part of the support ring is movable in a direction perpendicular to a plane including the outer rim and the arms of the support ring, that is, in the main axis direction of the microphone unit facing the front of the microphone. But, the central support part of the support ring essentially cannot move in a direction perpendicular to the main axis of the microphone unit facing the front of the microphone. Accordingly, even when the conventional support rings are used in the M-S type stereophonic microphone which is used on the camera as described before, the vibrationproof effect is obtained with respect to the mid microphone unit, but the vibrationproof effect is essentially not obtained with respect to the side microphone unit. Therefore, there is a disadvantage in that the vibrationproof effect as a whole with respect to the external vibrations is insufficient.